Ice bank control with voltage protection sensing

ABSTRACT

The present invention is an apparatus and method that regulates the size of an ice bank ( 50 ) and that prevents short cycling of the compressor ( 30 ) therefor and operation thereof at undesired voltages. A microprocessor based control circuit ( 10 ) includes a circuit for sensing line voltage ( 14 ) combined with an ice bank sensing circuit ( 18, 20 ). The ice bank sensing circuit is of the conductivity sensing type wherein the electrical conductivity between two probes (P 1 , P 2 ) is sensed. The microprocessor ( 16 ) continually monitors the probes (P 1 , P 2 ) to determine if refrigeration is needed or not, and continually senses the line voltage to determine if that voltage is within the design limits of the refrigeration compressor ( 30 ). The voltage sensing circuit ( 14 ) can also sense if power has been interrupted where the voltage drops to zero.

FIELD OF THE INVENTION

The present invention relates generally to electronic ice bank controlsand to voltage sensing controls.

BACKGROUND OF THE INVENTION

Ice banks that are formed on evaporators for providing a coolingreserve, as used in the beverage dispensing industry, are well known.The size of an ice bank is typically regulated by one or more sensorsplaced at critical positions around an outer perimeter thereof.Conductivity sensors are known and are used in this regard to determinethe presence of ice or water by virtue of the conductivity between apair of probes. Thus, if ice forms between the probes the sensedconductivity will be relatively low, and if water is present therebetween, the sensed conductivity will be much greater. Therefore, if iceis sensed, the ice bank is presumed to be of adequate size and therefrigeration compressor, that is used to cool the evaporator and formice thereon, can be shut off. Conversely, if water is sensed, thecompressor is turned on to build ice until ice is again sensed.Naturally, such controls have delay times programmed therein to preventdestructive short cycling of the compressor.

It is also well understood that it can be harmful to a compressor if itis made to run at a voltage that is outside, above or below, the voltagerange for which it is designed. This situation is common for beveragedispensing equipment used in remote areas where line voltage canfluctuate dramatically. Buck/Boost systems, that attempt to lower orraise the voltage, respectively, have been attempted, but without greatsuccess do to the complexity and cost thereof. Adding a voltage sensingsystem that can turn the compressor off if its voltage design limits areexceeded, is also a possibility. However, the cost of an additionalelectronic control can be unacceptable. Especially where such anadditional control would need to become a standard part of all suchdispensers, many of which will experience no need therefor. It is alsogenerally too expensive to provide such voltage sensing as a customfeature. Accordingly, it would be desirable to have a cost effectivecontrol for an ice bank that both regulates the size thereof, thatprotects the compressor against short cycling and from operating atvoltages outside its design specification.

SUMMARY OF THE INVENTION

The present invention is an apparatus and method that regulates the sizeof an ice bank and that prevents short cycling of the compressor andoperation thereof at undesired voltages. A microprocessor based controlcircuit includes a circuit for sensing line voltage combined with an icebank sensing circuit. The ice bank sensing circuit is of theconductivity sensing type wherein the electrical conductivity betweentwo probes is sensed. Thus, the microprocessor continually monitors theprobes to determine if refrigeration is needed or not, and continuallysenses the line voltage to determine if the voltage is within the designlimits of the refrigeration compressor. The voltage sensing circuit canalso sense if power has been interrupted where the voltage drops tozero.

In operation, the present invention will turn on the compressor if theice bank sensor indicates water is present between the probes, thevoltage is within operating limits and if a predetermined time delay haselapsed since the last compressor shut down. The compressor is turnedoff if, during operation thereof, the ice bank is of sufficient size,the voltage goes outside of design limits or there is a power failure.It can be appreciated that the voltage sensing circuit can be comprisedessentially of a relatively inexpensive voltage divider circuit of adedicated transformer. Therefore, the present invention utilizes theinexpensive combination of such a voltage sensing circuitry with aconductivity/ice sensing circuit to provide for an ice bank control thatis more protective of the compressor with respect to both short cyclingand operating at voltages outside the manufacturer's recommendedspecifications, than is found in prior art ice bank sensing controls.Since the improved control of the present invention is relativelyinexpensive, it can be used as a standard item rather than as a morecostly custom or add on feature.

DESCRIPTION OF THE DRAWINGS

A further understanding of the structure, function, operation, andobjects and advantages of the present invention can be had by referringto the following detailed description which refers to the followingfigures, wherein:

FIG. 1 shows an electrical schematic of the control of the presentinvention.

FIG. 2 shows a schematic diagram of the present invention.

FIGS. 3A and 3B show a flow diagram of the operational control of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The control system of the present invention is seen in FIG. 1 andgenerally designated by the numeral 10. Control 10 includes a powersupply circuit 12 including a transformer T1 connected to a powersource, in this example, of 115VAC. Power supply 12 provides for outputsof 18VAC, 24VDC and 5VDC, where D1 provides for the rectification of thecurrent from AC to DC. R4, R6 and C7 comprise a voltage detectioncircuit 14 wherein the voltage along the 24VDC line is sensed. Circuit14 is connected to a microprocessor 16 by pin 17. Those of skill willunderstand that R4 and R6 function as a voltage divider circuit to bringthe detected voltage changes within a range that is useful tomicroprocessor 16. Of course, microprocessor 16 also includes an analogto digital converter for converting the DC signal from circuit 14 to ausable digital form. In the present example, microprocessor 16 is aMicrochip model PIC16C11.

Ice bank detection probes P1 and P2 form part of an ice probe circuit18. R22, R2 and Q5 comprise a signal conditioning circuit with an inputto pin 1 of microprocessor 16. This conditioning is needed as the probeinput impedance is generally too high for microprocessor 16. Probe P1 isconnected by line L5 to probe signal circuit 20, and output pins 9 and10 are connected to circuit 20 by lines L6 and L7. Resistors R7, R8, R9and R10 along with diode D3 and transistors Q1 and Q2 provide for a 5VDCsignal and a −5VDC signal to L5. The −5VDC is provided by power supplycircuit 22.

A clock circuit 24 is provided and connected to microprocessor 16 byinput pins 15 and 16. A power relay switching circuit 26 includes arelay 28 for operating a switch K1. Switch K1 is connected to acompressor 30. Pin 8 of microprocessor 16 is connected to circuit 26 forcontrolling the operation of relay 28. Pin 6 can be used to detect theline power interruptions.

As seen in the block diagram of FIG. 2, control 10 is used in thecontext of a beverage dispensing machine 40. As is known in the artdispenser 40 includes a water bath tank 42 containing a volume of waterand an evaporator 44. Evaporator 44 is part of a mechanicalrefrigeration system including compressor 30, a plurality of refrigerantlines 45, a condenser 46, a condenser cooling fan 48, and an expansionvalve 49. As is well known in the art, the refrigeration system operatesto cool evaporator 44 to form an ice bank 50 thereon. Probes P1 and P2are seen within dashed circle 52 in enlarged form, relative to ice bank50. Those of skill will appreciate that probes P1 and P2 are inactuality positioned at a distance from evaporator 44 to which it isdesired that ice bank 52 is to grow. As is also known, a plurality ofbeverage lines 54 extend through bath 42 and deliver potable beveragefrom sources thereof, not shown, to one or more beverage dispensingvalves 56. Thus, ice bank 50 provides a cooling reserve for the heatexchange cooling of the beverages as they pass through lines 54 so thatcompressor 30 need not run all the time that cooling is required. Alight 58 indicates when compressor 30 is running.

The general operation of electrical conductivity based ice bank controlsis well known in the art. The conductivity approach takes advantage ofthe substantial known difference between the electrical conductivity ofwater and that of ice. Thus, where the sensed electrical conductivity islow due to essentially no current flow between the probes, ice isindicated as ice is a poor electrical conductor. Conversely, whencurrent is readily conducted between the probes, then water therebetween is indicated as the conductivity thereof, in most conditions, isdramatically higher than that of ice. Accordingly, when a highconductivity is sensed water between the probes is indicated. As aresult thereof, it is assumed that the ice bank has eroded to a pointthat the refrigeration system must be turned on to build the ice bank upto a size that maintains an adequate cooling reserve. Once the probesare again covered with ice, the lower conductivity is sensed and it isassumed that the ice bank has grown back to its desired size and furtherrefrigeration can be stopped.

In the present invention, a current is passed between probes P1 and P2from line L5 by operation of circuits 18 and 20. The present inventionuses the known convention, as represented specifically by circuit 20, ofalternating the voltage there between to eliminate a net electricalplating or deposition on either probe P1 or P2. Thus, microprocessor 16serves to control that voltage switching. As described above, when theconductivity between probes P1 and P2 is sensed as high bymicroprocessor 16, water there between is indicated and compressor 30can be turned on. Conversely, when the sensed electrical conductivity islow, ice between probes P1 and P2 is indicated, and compressor 30 can beshut down.

To get a better understanding of the specific mode of operation of thepresent invention with respect to the control and interrelation ofvoltage sensing and conductivity sensing, attention is drawn to the flowdiagrams 3A and 3B. At block 60 compressor 30 is off and at block 62microprocessor 16 is continually reviewing the conductivity data asproduced by probes P1 and P2 and circuit 18. If the conductivity readingindicates that water is present, then the yes arrow is followed fromblock 62 to block 64. If ice is indicated, then no further cooling isrequired and the system returns to compressor off block 60. At block 64a preset time delay is contained in the controlling software, as isknown in the art to prevent the startup of compressor 30 prior to theelapse of a predetermined time period. That time period, such as threeminutes, serves to protect compressor 30 from destructive short cycling.If this protective predetermined time period has timed out, then thecontrol logic proceeds to block 66. It can be appreciated that voltagedetection circuit 14 can sense if there has been a power interruptionwhere the sensed voltage drops to zero. Thus, the control of the presentinvention has a further short cycling safeguard represented by block 66where, if power is interrupted, the above predetermined time delay isalso utilized to prevent premature start up of compressor 30. If thepredetermined time period has also timed out since the last powerinterruption, then at block 68, circuit 14 is used to determine if thesensed line voltage is within the recommended operating limits ofcompressor 30. If the sensed voltage is within such parameters, then atthis point, block 70, compressor 30 can be turned on. After a time delayrepresented by block 71, microprocessor 16 continually monitors the linevoltage, whether or not there has been a power outage and whether of notprobes P1 and P2 are indicating that cooling is still required. Theforegoing monitoring is represented by blocks 72, 74 and 76respectively. Thus, if after the time delay of block 71, the linevoltage goes out of range, or the power is interrupted or probes P1 andP2 become covered with ice and no further growth of the ice bank isrequired, then the system herein returns to the compressor off conditionof block 60.

Those of skill will appreciate that the control of the present inventioncan provide for both line voltage compressor protection and ice banksensing and management at a very minimal cost over the cost of ice bankmanagement alone. Thus, it is cost effective that the control herein beused as a standard item rather than as a custom control only for thebeverage dispensing machines thought to have the greatest likelihood ofencountering voltages outside of the compressor's design limitations.

What is claimed is:
 1. A control for operating a beverage dispensingmachine, the beverage dispensing machine having a refrigeration systemincluding a compressor for cooling an evaporator positioned in a waterbath for forming an ice bank thereon, the control comprising: a voltagesensing circuit for determining the voltage of an incoming lineproviding power to the compressor, an ice bank sensing system includingconductivity probes positioned within the water bath and a conductivitysensing circuit for determining the conductivity between the probes andthe compressor operated to provide for cooling of the evaporator forforming ice thereon when the voltage sensing circuit determines that theincoming line voltage is within design limits of the compressor, andwhen the ice bank sensing system determines that further formation ofice is required and when a predetermined time delay has timed out sincethe compressor last operated.
 2. The control as defined in claim 1 andthe voltage sensing circuit also sensing for a power outage and notrunning the compressor for the predetermined time period subsequent tothe sensing of a power outage.